Free radicals have been implicated in the pathology of some disease states for a number of years. In addition, a school of thought considers free-radical damage an important factor in aging. Precise biochemical markers have been lacking and this has hampered our understanding of the free-radical phenomenon and its correlation to diseases. The isoprostanes (iPs) are a new class of natural products isomeric with prostaglandins (PGs) and produced in vivo by a non-enzymatic free-radical-induced peroxidation of polyunsaturated fatty acid. In the case of arachidonic acid (AA), for example, four classes of iPs can be produced. Because of the specific structural features distinguishing them from other free radical-generated products, e.g. hydroxyeicosotetraenoic acids (HETEs), etc., the iPs can provide an exclusive and selective index for the oxidant component of several inflammatory and degenerative diseases. Encouraging preliminary results show a strong correlation between the urinary levels of selected iPs (iPF2a-VI, 8,12-iso-iPF2a-VI), and the severity of Alzheimer's disease and atherosclerosis. Identification of new selected iPs in biological fluids, in particular iPs derived from AA, docohexaenoic acid (DHA) and eicosapentaenoic acid (EPA) is planned. Methods to measure these iPs will be developed. The accurate measurement of these iPs as a non-invasive index of lipid peroxidation in diseases such as Alzheimer's and atherosclerosis will be undertaken. To achieve this goal a combination of the total synthesis of these iPs, their deuterated analogs, and the development of GCIMS and LC/MS/MS methodology will be accomplished. In an effort to improve our understanding of the free radical involvement in diseases, the mechanism of formation of iPs will be investigated. Analysis of iP production at the in vitro phospholipid and cellular levels will be initiated. The question of metabolism and enantiomerism of iPs will be examined. A preliminary look at the contribution of enzymes to free-radical formation is planned. The biological evaluation of new iPs, in PG receptor assays and other related systems will be undertaken.